Raymond Ruyer was first interested in mechanism and relativity. War and captivity gave this philosopher the occasion to meet biologists and to discover the rich material he needed to develop his “psycho-biology”. Yet the main theses of Neo-finalism are the result of a long evolution with its origins in Ruyer’s doctoral thesis. First a strong defender of actualist positions, Ruyer began to consider the necessity of admitting a virtual depth for life in the middle of the thirties, and he reached the thickness of meaning and signification in the articles he published just before the Second World War. He then realized he had to admit, beyond the drought of the causal structuration of the partes extra partes, a psycho-biological lining for the mere extent of matter.